Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, United States.
J Am Chem Soc. 2012 May 23;134(20):8633-45. doi: 10.1021/ja3019498. Epub 2012 May 9.
We present a comprehensive experimental study of the formation and activity of dealloyed nanoporous Ni/Pt alloy nanoparticles for the cathodic oxygen reduction reaction. By addressing the kinetics of nucleation during solvothermal synthesis we developed a method to control the size and composition of Ni/Pt alloy nanoparticles over a broad range while maintaining an adequate size distribution. Electrochemical dealloying of these size-controlled nanoparticles was used to explore conditions in which hierarchical nanoporosity within nanoparticles can evolve. Our results show that in order to evolve fully formed porosity, particles must have a minimum diameter of ∼15 nm, a result consistent with the surface kinetic processes occurring during dealloying. Nanoporous nanoparticles possess ligaments and voids with diameters of approximately 2 nm, high surface area/mass ratios usually associated with much smaller particles, and a composition consistent with a Pt-skeleton covering a Ni/Pt alloy core. Electrochemical measurements show that the mass activity for the oxygen reduction reaction using carbon-supported nanoporous Ni/Pt nanoparticles is nearly four times that of commercial Pt/C catalyst and even exceeds that of comparable nonporous Pt-skeleton Ni/Pt alloy nanoparticles.
我们对去合金化的纳米多孔 Ni/Pt 合金纳米粒子在阴极氧还原反应中的形成和活性进行了全面的实验研究。通过解决溶剂热合成过程中的成核动力学问题，我们开发了一种在保持适当粒径分布的同时，能够在较宽范围内控制 Ni/Pt 合金纳米粒子尺寸和组成的方法。电化学去合金化这些尺寸可控的纳米粒子，用于探索纳米粒子内分级纳米多孔性可以演变的条件。我们的结果表明，为了使完全形成的孔隙演变，粒子的最小直径必须约为 15nm，这一结果与去合金化过程中发生的表面动力学过程一致。纳米多孔纳米粒子具有直径约为 2nm 的链节和空隙，具有通常与更小粒子相关的高表面积/质量比，以及与 Pt 骨架覆盖 Ni/Pt 合金核一致的组成。电化学测量表明，使用碳载纳米多孔 Ni/Pt 纳米粒子的氧还原反应的质量活性是商业 Pt/C 催化剂的近四倍，甚至超过了可比的非多孔 Pt 骨架 Ni/Pt 合金纳米粒子。
